cam, it can be tricky when you can't allign the sight housing in your peep. makes it tough to do the same thing every time, so the following may be useless to you.

anyway, if your 20 pin is dead on with field points - back up to 30 and shoot a dot towards the top of your target using your 20 yard pin a few times.(obviously your arrows will be low of what you're aiming at - that's why i said towards the top)if your arrows are going to the left of the dot you're aiming at, then move your rest a hair right (or vice versa). then you'll have to re-sight in at 20. when that's done go back to 30 and do it again. when you're done, if you use your 20 pin at 20 yards the arrow should be dead on, and when you back up and keep using your 20 pin your arrows should fall directly below the dot you're aiming at. then you'll know you've got your arrow rest set to the correct place right and left. then go up to 20 yards and shoot a horizontal line across your target - use tape or something - if you're shots are more than 1/2"-1" above or below the line you may need to adjust your nocking pt. i would say tiller, but lets just go with the nock pt. instead.

like i said though, if you just can't get any reference with the peep and sight, this may not help as much as it should. a larger peep should help, or an extension bar for your sight - but a bigger peep would be cheaper.